Thread pull-off mechanism for sewing machines



March 30, 1948 R, WOOD 2,43s,s33

THREAD PULL-OFF MECHANISMS FOR SEWING MACHINES Filed Aug. 21, 1945 2Sheets-Sheet l March 30, 1948. A. R. WOOD THREAD PULL-OFF" MECHANISMSFOR SEWING" MACHINES 2 Sheets-Sheet 2 Filed Aug. 21, 1945 BUTTON/IDLESL/T Patented Mar. 30, 1948 THREAD PULL-OFF MECHANISM FOR SEWINGMACHINES Alfred R. Wood, Bridgeport, Conn, assignor to The SingerManufacturing Company, Elizabeth, N. J a corporation of New JerseyApplication August 21, 1945, Serial No.-61 1,;7 2 4 1 Claims.

This invention relates to buttonhole sewing machines, more particularlycf the automatic lock-stitch straight type, which is adapted to producehigh quality buttonholes used most cqllmmonly in mens shirts, collars,cuffs and the li e.

"The type of stitch used to form this high quality buttonhole isgenerally referred to in the trade as the pyramid-purl lock-stitch. Inthis type of stitch-i'for-mation, the needle-thread take-up is requirednot only to draw up the needle-thread loops after they have beeninterlocked with the bobbin-thread, but also to draw such loops entirelythrough the work, pulling loops of bobbin-thread through to the upperside of the Work, so that in the finished seamthe needlethread will liein substantially a straight line intermediate the rows of zigzagneedle-punctures, while loopsof bobbin-thread emergefrom theneedle-punctures at the upper side of the work and embrace the straightneedle-thread. To .efiect this stitch-formation, it is necessary thatthe tension imposed upon the bobbin-thread be light, while the tensionimposed upon the needle-thread be very strong. To further assist inproperly concatenating the needleand bob bin-threads, it has been commonto employ a bobbin-thread pull-off mechanism, which is designed tooperate once during each stitch-forming cycle to pull from the bobbin a.length of thread to be absorbed into the stitch when the needle-threadloop is pulled up by the usual take-up. The presence of this slackbobbinthread available after the pull-off member is retracted permits areduction in the amount of tension required on the needle-thread. Thisis advantageous inasmuch as it minimizes thread b ea a Thesuccessfuloperation of the bobbin-thread pull-01f is materially affected by theinherent elasticity ef the thread being used. The effect of using abobbin-thread having considerable elasticity, or one in whichtheelasticity varies somewhat throughout its length, is that unequallengths of thread are pulled from the bobbin u ing the fo mation o hetche n t utto-nhele. The result of a variation in the length of threadpulled off is that, in the finished buttonhole, the needle-th ead liesin a line which is wavy relative to the buttonhole slit. This defect isimmediately discernible to the naked eye and t r fe e ma er al yreduc st e q y of the finished bu tonh l herefqre, it s th pri ary b ect of thpresent inv ntion to pro id a imp otedmlleqfl mechanism which iseffective to draw a uniform length of bobbin-thread .from the supplyduring each stitch-forming cycle, whereby a finished buttonhole isproduced having the p ramid-pu l formed in a straight line substantiallyparallel to and uniformly spaced from the buttonhole slit.

With the above and other objects in view, as will hereinafter appear,the invention comprises the devices, combinations and arrangements ofparts hereinafter set .forth and illustrated in the accompanyingdrawings of a preferred embodiment of the invention, from which theseveral features of the invention and the advantages attained therebywill be readily understood by those skilled in the art.v

In e a m a n draw n s:

Fig. 1 represents a front .elevational view, partly in section, of abuttonhole, machine equipped wit my i prove bob i -thread P 1 oifmechanism. e

Fig. 2 represents a bottom plan yiew, partly in section,showingtheconnections for actuating the pull-off blade.

Fig. 3 represents avertical sectional view taken substantially along theline (3+3, 1, illustrating the mechanical opener mechanism for theloop-taker and also the 1 68. 5 employed for rendering the threadpull-01f Lblade inefiective.

Fig. 4 represents a fragmentary view of a buttonhole, showing the manner.in which the needle-thread and bobbin thread are cpncatenated to form apyramid-purl.

Fig. 5 represents a. vertical sectional view taken substantially alongthe line 5-75, Fig. 3.

Fig. 6 represents anenlarged top plan .view of the loop-takerthread-case and carrier therefor,

showing the desired shape oi the otht iqllstraining member and the:leaf-springpby which the bobbin-thread is maintained in position insaid rotation-restraining member.

Fig. '7 represents an enlarged leitside elevational view, partly insection, of the c-shaped thread-guiding projection on, the thread-casebetween the spaced limbs oi which operates the bobbin-thread pul1=qffblade.

Fig. 8 represents a sectional view taken substantially along the line.898, Fig. 3,

Fig. 9 represents a right side elevational View, partly in section, ofthe ,stitcheiorming instrumentalities, showing the bobbin-threadpull-off blade in its maximumthread pull-off position.

Fi 10 is a view similar to 9,.but with the Dull-o1? blade shiftedlaterally to its ineffective p ition. in which position the blade is outof the range of the lead of the bobbin-thread between the spaced limbsof the C-shaped threadguiding projection on the thread-case.

Referring to the drawings, the machine chosen for the purposes of thepresent disclosure is constructed substantially in accordance with thatforming the subject of my United States Patent No. 241L493, issuedNovember 19, 1946, and has a frame including a bed ll provided with asupporting lug l2. J ournaled in a bushing 13 pressed into thesupporting lug I2 is a rotary loop-taker shaft l4 geared to be operatedby an arm-shaft (not shown) at a speed twice that of the armshaft. Asclearly shown in my above mentioned patent, the arm-shaft is connectedat the headend of the machine to endwise reciprocate a thread-carryingneedle 45 which is adapted to be vibrated in a direction crosswise ofthe bed ll. Cooperating with the needle [5 in the formation oflock-stitches is a loop-taker, indicated generally as l5, of the rotarylock-stitch type, which loop-taker is fast on the rotary shaft M.

The work to be buttonholed is adapted to be held in a work-clampcomprising the usual lower work-plate l1 and the upper clamp-foot 18,Fig. 1. The work-clamp is slowly moved in step-bystep fashion under theendwise reciprocatory and laterally vibratory needle 15, and relative tothe usual needle-aperture l9 in the throat-plate 20, first away from themachine-standard and then towards the machine-standard to cause thefirst and second rows of side zigzag stitches to be laid side by side inthe work. The work-clamp derives its sten-by-step movements from theusual feedcam 2| through a link 22, Fig. 2, connected at one end to aslide-block 23 associated with the lower work-plate I! and operable in aslideway 24 provided in the bed H.

As previously-mentioned. the stitch-forming mechanism of the machineillustrated comprises the endwise reciprocatory and laterally vibratorythread-carrying needle I5 and the complemental rotary hook I6. Therotary hook is adapted to seize the thread-loop presented by the needleand expand such loo for passage about the under thread-mass contained inthe stationary thread-mass enclosing means of the rotary hook. Thethread-mass enclo ing means shown in the drawings forms the subject ofmy United States Pa ent No. 2.419.698 dated April 29, 1947, and

therefore only sufficient reference will be made in this case to thismeans as will be reouired to give an understanding ofthe operation ofthe bobbin-thread pull-ofi'. Suffice it to say that the thread-massenclosing means comprises a cupshaped carrier-member 25 and atelescopically disposed thread-case 25, defining between them athread-mass cavity into which is inserted the usual bobbin or cop. Torestrain the threadmass enclosing means against rotation with the rotaryloop-seizing beak of the loop-taker, the carrier-member 25 has extendingupwardly from itsperiphery a substantially C-shaped projection 21, theupper portion of which is adapted to extend between the free ends of apair of stop-plates 28 and 29 (Fig. 1), adjustably secured to the bed IIof the machine-frames The C-shaped projection 2'! is verticallychanneled to receive a, correspondingly shaped upstanding projection 39formed on the thread-case 25.

As fully disclosed in my above mentioned U. S. Patent No 2,419,698 andshown in Figs. 9 and 100i this case, the bobbin-thread emerging from theusual thread-aperture in the thread-case 26 is directed beneath atension-spring 3!, then behind a thread-guiding pin 32, upwardly througha threading-slit 33 provided in the thread-case projection 30, andthence beneath the free end of a leaf-spring 34 fastened to the upperlimb 35 of the projection 30. As will be seen in Figs. 9 and 10, thethread-guiding pin 32 and the leafspring 34 function to maintain thebobbin-thread adjacent theinner end of the threading-slit 33, whichposition of the thread is advantageous as regards the successfuloperation of the bobbinthread pull-oil now to be described. Also, theleaf-spring 34 serves to lightly nip the bobbinthread and thus preventthe accidental unthreading of the upper limb 35.

Disposed to operate between the spaced bobbin-thread-directing guidesdefined by the upper and lower limbs 35 and 35 of the C-shapedprojection 3B is a curved thread pull-off blade 31 having a thread-camedge 38 formed adjacent its free end. At its other end, the pull-offblade 3'! merges into an offset shank 39 (Fig. 3) provided with anelongatedhole 4e and an inturned positioning lip 4|; the lip beingadapted to enter a slot 42 formed in the outer end of a carrierlever 43which embraces and is freely journaled at its inner end on. the exposedend of the hookshaft bushing I3. A clamp screw 44 passing through theelongated hole 40 and threaded into i "ing position between the limbs 35and 36 of the G-shaped projection 30. When the pull-on blade 31 isadvanced from its retracted position, shown in full lines in Fig. 5, toits advanced position, shown in dotted lines in the same figure, thethread-cam edge 38 is adapted to contact and deflect laterally theportion of the bobbin-thread leading from the lower to the upper limb ofthe C-shaped projection 39 and form a bight in the thread between thelimbs of the projection, in the manner shown in Fig. 9. The blade 31, informing the bight in the bobbin-thread, draws from the supply within thethread-case 26 a length of thread sufficient to form a bobbin-threadloop of a size such that it may be pulled through to the upper side ofthe work (Fig. 4), so that in the finished seam the needle-thread willlie in substantially a straight line adjacent the buttonhole slit. Itwill be noted that the limbs 35 and 33 of the C-shaped projection 39 arerather closely spaced apart. This is advantageous for the reason thatthe bobbin-thread extending between the limbs 35 and 36, as shown indotted lines in Fig. 9, is relatively short. It is, in fact, so shortthat, when the thread-cam edge 38 of the pull-off blade engages thethread, any inherent elasticity in the thread does not militate againstthe drawing of a uniform length of thread from the supply during eachstroke of the pull-off blade.

The mechanism for actuating the bobbinthread pull-oil blade 31preferably comprises a counterbalanced crank 45 (Fig. 5) having acrank-pin 46 connected by a link 41 to a pin 48 threaded into thecarrier-lever 43. The counterbalanced crank 45 is carried on the outerend of a horizontally disposed rotary actuating shaft 49 journaled in abearing bushing 59 pressed into the supporting lug l2. Secured on theother end of the actuating shaft 49 is a gear 5| in mesh with ahalf-size gear =52 fast on the -hook--shaft 14. Through the mechanismjust described, rotation -of the hook-shaft l4 imparts to the actuatingshaft 49, through the gearing -51 and 52, "rotary rotated, thecounterbalanced crank 45 imparts to thecarrier-lever 43, through thelink 4'Iand pin 43,a motion causing the carrier-lever to oscillate aboutthebushing 1-3. The pull-off blade 31,

which is secured to the carrier-lever, is thereby swung about an axiscoaxially with the rotary hook l6 and is 'timedto begin its advance asthe needle is starting down and to completeits advance at about the timethe needle reaches'the limit of its downstroke. The pull-off blade 31dwells in its advanced position '(dotted lines in Fig. while the needleis throwing out a loop of upper thread for seizure by the rotary hookHi. The pull-off then retracts so that slackbobbinthread is available tobe absorbed into the next stitch when the needle-loop ispulled upby theusual needle-thread take-up mechanism. At the time of initial engagementof the-pull-ofi' blade 37 with the bobbin-thread, said blade is movingat a speed considerably less than that of the rotary hook l6. This factcoupled with thegrad ual incline of the thread-cam edge 38, results inthe pull-off blade engaging the bobbin-thread with a. smooth action,thusavoiding a jerking of the bobbin-thread and minimizing any tendencytoward overrunning or spilling of thread'bythe bobbin or cop.

Provision is made for rendering the pull-off blade "31 ineffectiveduring the sewing ofthebarring stitches at each'end of the buttonho-le;so that the locking points of these stitches will not be pulled throughthe work as are the sidestitches of the buttonhole. To thisend,-theworkingposition of the carrier-lever 43 is shifted longitudinallyof the bushing l3 so that the free end of the pull-off .bladewill,'in its advance miss the bobbin-thread, as shown in Fig. 10. Toefiect this shifting of the pull-ofi blade 31, the hub of thecarrier-lever .43 is formed with a circumferential groove 53 which is"entered by the half round recessed portion of an arm -54 '(Fig. 18) ona slide-shaft 55 journaled in thesupporting lug 1 on a stud 59 threadedinto the .bed [I The lever 58, at itsfree end, is longitudinallyrecessed, as at 60, to adjustably receivea cam-,followerlil having anelongated aperture 62 through which passes a clamping screw 63 threadedinto thelever 5B. The camefolloweris disposedtobe engaged by acam-section 64 secured by screws'54' on'the feed-cam "2|. While only.One cam-section is shown, it will be understood that 'twocam-sec-.tions are employed, one for each barring operation. 'In the operationof the machine, the "feedcam is ,rotated in the direction of the arrowin Fig.2, once during each complete buttonholing cycle. Whenthecam-section B4 on thefeed-cam 2i engages the cam-follower 6|, theswing-lever 58 ismoved in a direction away-from the feed-- cam, causingthe roller 51 to move into engagement with the head .56 of theslide-shaft 5,5 shift the same outwardly against the action of acoil-spring 65 acting between a collartfi on-the slide-shaft and thesupporting lug 12. When -rier 25 on thecast-on side thereof.

the slide-sha'ft ts 'isishlfted, the. carrier-lever :43,

ithrough the mediumibftheiarm 754, is moved out- =-wardly on the bearingbushing l3 and to the -=extent that the point ofthe pull-off bladei3'lentirely miss'es :the bobbin-rthread (Fig. 10) and no bobbin-thread ispulled off during the formation of the barring stitches. After thecompletion of thelast barring :s'tit'c'h and the camsectionifi l hasmoved beyond the cam-:follower 61, the coilspring acts to return thepull-off blade 31 to its efiectivepo'siti'on, which position isdetermined 'by the'hub of the arm 5 striking the supporting lug :12.Asshown'inFig. 3, the pin-48 slides relative to the upper end-'of-thelink 41 during the shifting of the pull-off blade and, consequently, thedriving -relationship of the pull-off bladeactuatin'g mechanismds-notinterrupted. It will be understood that the timing of the shaft of thepull-01f blade fromeffective to ineffective position adapted --to behoused in "a thread-mass enclosing means including; athread-case "26 anda carrier 25 therefor; the thread-case and carrier beingrestrainedagainst-rotation with the rotary loopta-ker 18 by means of theloosely interengaging projection 2-1 and stop-plates *28 and 29. The

thread-case audits carrier have-a normal tendency to rotate with --theloop-taker, thereby causing therotation-restraining projection 21 tobearIn order to obtain a free passage 'on each side of the projection 21 forthe --unolostructed "free travel of the needle-thread loop-aboutthethread-case and its carrier during stitch-formation, the thread-case andits carrier are=intermittently oscillated, for a limited extent, ina--di-re'ction opposite'to the direction "of rotation of the loop-taker.This oscillation is effected by means of a mechanical opener which formsthe subject ofmy divisional application Serial No. 678,618, filed June22, 1946, and-comprises an opener-arm 6'! (Figs. 1 and 3) which isadjustablyclamped at its lower end in a :split socket-member 68 fast onthe outer end of a rock-shaft -Bil journaled in a horizontal bushing 10presseddn tothe supporting lug l2. At its upper end, theopener-arm 6'!isbent, as at ll,

to provideahook-shaped end extending toward the thread-case '26; thehook-shaped end being -notched,-as at l-2, "Fig. 1, toform spacedresilient fingers 13 "adapted to enter an opener-arm receiving pocket 14formed in the thread-case car- The fingers "are preferablyshaped'so'that there is asmooth cam-like "initial :engagement of theupper fin- .ger with eneside o'f the threadcase carrier pocket 14 toi-nitiate'auoscillation of the thread-case carriei in a'directionreverse to the direction of rotation of the hook-body, and thatfollowing tained ---stationary substantially midway between thestop-plates2i3 and 2-8. The spaced resilient fingers l3 serve to providea relatively noiseless mechanical-openenas well as one which maintainsthe rotation-restraining projection onlthe "thread-mass enclosing meansstationary and in position such that an open thread passage existson'both sides-of the projection for the ireeunobstructed travel of theneedle-thread loop.

. understood that I have invented a bobbin-thread pull-off mechanismwhich is accurate in its operation, drawing from the supply an equallength of thread during each stitch-forming cycle, regardless of thedegree of elasticity inherent in the thread. The upstanding C-shapedrotationrestraining projection on the thread-case carrier providesclosely spaced thread-confining limbs between which operates the threadpull-off blade. In addition, the rotation-restraining projectionprovides a surface which functions to retard one limb of theneedle-thread loop as it is being cast off the thread-case, and thisretardation minimizes twisting of the thread comprising the loop,thereby preventing the formation of loops or knots in the pyramid-purlof the buttonhole. Furthermore, since the upper limb 35 of therotation-restraining projection is positioned adjacent the bottom of thethroat-plate 2!], the short cut end of the bobbin-thread, which isproduced by the actuation of the usual threadcutting devices followingthe completing of the buttonhole, is retained by the slight nippingaction of the leaf-spring 34 near the work and not permitted to dropdown out of control. This control of the bobbin-thread insures theproper operation of the pull-off mechanism on the first stitch of thenext buttonholing cycle.

Having thus set forth the nature of the invention what I claim hereinis:

1. A sewing machine having, in combination, a thread-carryingreciprocatory needle, a circularly moving loop-taker cooperatingtherewith, a bobbin-thread-mass enclosing means journaled in saidloop-taker, a rotation-restrainingprojection on said thread-massenclosing means having a pair of spaced thread-directing guides, and athread pull-off member adapted to engage the bobbin-thread between saidthread-directing guides during each stitch-forming cycle.

2. A sewing machine having, in combination, a thread-carryingreciprocatory needle, a circularly moving loop-taker cooperatingtherewith in the formation of lock-stitches, abobbinthread-massenclosing means journaled in said loop-taker andrestrained against rotation therewith, a projection extending from saidbobbinthread-mass enclosing means and providing a pair of spacedthread-directing guides, and a thread pull-off member arranged to engagethe bobbin-thread between said thread-directing guides once during eachstitch-forming cycle.

3. A two-thread sewing machine having, in combination, a thread-carryingreciprocatory needle, a rotary loop-taker having a loopeseizing beakcooperating with said needle in the formation of lock-stitches, abobbin-thread-mass enclosing means journaled in said loop-taker andrestrained against circular movement therewith, a pair ofbobbin-thread-directing guides disposed outside the field of action ofthe loop-seizing beak of said rotary loop-taker, and a thread pull-01fmember arranged to engage the bobbinthread between said thread-directingguides to draw thread from the bobbin once during each stitch-formingcycle. I

4. A two-thread sewing machine having, in combination, a thread-carryingreciprocatory needle, a circularly moving loop-taker having aloop-seizing beak cooperating with said needle in the formation oflock-stitches, a bobbin;

thread-mass enclosing means journaled in said loop-taker and restrainedagainst rotation there- With, said bobbin-thread-mass enclosing meansincluding a thread-case having a cylindrical side wall, a projectionextending from said threadcase and providing a pair of spaced limbsdisposed beyond the confines of said cylindrical side wall, athread-directing guide in each of said limbs, and a thread pull-ofimember adapted to engage the bobbin-thread between said threaddirectingguides once during each stitch-forming cycle.

5. A sewing machine having, i combination, a thread-carryingreciprocatory needle, a circularly moving loop-taker cooperatingtherewith in the formation of lock-stitches, a bobbinthread-massenclosing means journaled in said loop-taker, a rotation-restrainingprojection on said bobbin-thread-mass enclosing means terminating insubstantially C-shape at it free end, thereby defining a pair of spacedlimbs each having a thread-directing guide, and a thread pulloff memberadapted to engage the bobbin-thread between said thread-directing guidesto draw thread from the bobbin once during each stitchforming cycle.

6. A sewing machine having, in combination, a bed fitted with athroat-plate, a thread-carrying reciprocatory needle, a circularlymoving loop-taker cooperating with said needle in the formation oflock-stitches, a bobbin-thread-mass enclosing means journaled in saidloop-taker and restrained against circular movement therewith, a firstbobbin-thread directing guide disposed adjacent saidthroat-plate, meansfor preventing the accidental unthreading of said first threaddirectingguide, a second bobbin-thread-directing guide spaced from said firstbobbin-threaddirecting guide, and a thread pull-oil" member arranged toengage the bobbin-thread between said first and secondbobbin-thread-directing guides to draw thread from the bobbin onceduring each stitch-forming cycle.

7. A sewing machine having, in combination, a bed fitted with athroat-plate, a thread-carrying reciprocator needle, a circularly movingloop-taker cooperating with said needle in the formation oflock-stitches, a bobbin-thread-mass enclosing means journaled in saidloop-taker and restrained against circular movement therewith, a firstbobbin-thread directing guide disposed adjacent said throat-plate, aleaf-spring cooperating with said first thread-directing guide forpreventing accidental unthreading of said guide, a secondbobbin-thread-directing guide spaced from said firstbobbin-thread-directing guide, and a thread pull-oif member arranged toengage the bobbin-thread between said first and secondbobbin-thread-directing guides to draw thread from the bobbin onceduring each stitch-forming cycle.

8. A sewing machine having, in combination, a bed having a throat-plate,means providing a rotation-restraining notch positioned adjacent saidthroat-plate, a thread-carrying reciprocatory needle, a circularlymoving loop-taker having a loop-seizing beak cooperating with saidneedle in the formation of lock-stitches, a bobbinthread-mass enclosingmeans journaled in said loop-taker, a rotation-restraining projection onsaid bobbin-thread-mass enclosing means and disposed to enter the notchadjacent said throatplate, a first thread-directing guide provided onsaid rotation-restraining projection adjacent said throat-plate, asecond thread-directing guide on said projection spaced from said firstthread- -directing guide, and a thread pull-oil member adapted to engagethe thread intermediate the firstand second thread-directing guides.

9. A sewing machine having, in combination, a thread-carryingreciprocatory needle, a circularly moving loop-taker cooperatingtherewith in the formation of lock-stitches, a bobbin-threadmassenclosing means journaled in said looptaker, a rotation-restrainingprojection on said bobbin-thread-mass enclosing means and having spacedlimbs, an open-sided threading-slit cut into said spaced limbs 50 thatthe closed end of the threading-slit is adjacent the ends of the limbs,means for maintaining the bobbin-thread adjacent the closed end of saidthreading-slit, thereby to provide spaced bobbin-thread-directingguides, and a thread pull-off member adapted to engage the bobbin-threadbetween the limbs of said rotation-restraining projection.

10. A sewing machine having, in combination, a thread-carryingreciprocatory needle, a rotary loop-taker cooperating therewith in theforma- 10 tion of lock-stitches, a bobbin-thread-mass enclosing meansjournaled in said loop-taker, a rotation-restraining projection on saidbobbin-v thread-mass enclosing means terminating in substantiallyC-shape at its free end to provide spaced limbs, an open-sidedthreading-slit formed longitudinally of said limbs and ending short ofthe ends of said limbs, means associated with each of the limbs formaintaining the thread in the closed end of said threading-slit, and athread pull-off member adapted for engaging the thread between the limbsof the rotationrestraining projection.

ALFRED R. WOOD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

